A MERV rating is a measurement scale designed by the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) to report the effectiveness of air filters in more detail than just a filters ability to capture larger particles between 0.3 and 10 microns (µm) . The MERV value ranges from 1 to 16, with higher MERV values corresponding to a greater percentage of particles captured on each pass. The MERV rating is derived from a test method developed by ASHRAE, and it represents the worst-case performance of a filter when dealing with particles in the range of 0.3 to 10 micrometers. The table below shows the MERV values by particle size:
| MERV | Minimum particle size | Typical controlled contaminant | Typical application |
|---|---|---|---|
| 1-4 | 3.0 - 10.0 | less than 20% | Residential window AC units |
| 5 | 3.0-10.0 | greater than or equal to 20% | Residential and commercial buildings |
| 6 | 3.0-10.0 | greater than or equal to 35% | Superior residential and commercial buildings |
| 7 | 3.0-10.0 | greater than or equal to 50% | Better residential and commercial buildings |
| 8 | 3.0-10.0 | greater than or equal to 70% | Better commercial buildings |
| 9 | 1.0-3.0 | greater than or equal to 85% | Hospitals and general surgery |
| 10 | 1.0-3.0 | greater than or equal to 85% | Better commercial buildings |
| 11 | 0.3-1.0 | greater than or equal to 95% | General surgery |
| 12 | 0.3-1.0 | greater than or equal to 98% | Hospitals and clean rooms |
| 13 | 0.3-1.0 | greater than or equal to 98% | Pharmaceutical manufacturing |
| 14 | 0.3-1.0 | greater than or equal to 99% | Nuclear power plants |
| 15 | 0.3-1.0 | greater than or equal to 99% | Electronics and computer manufacturing |
| 16 | 0.3-1.0 | greater than or equal to 99.97% | Clean rooms |
A higher MERV rating means that the filter can trap smaller air particles, and the best MERV rating for residential use is the one that adequately cleans the air in your home without decreasing the air flow and straining your HVAC equipment. Generally, a MERV rating between 6-13 meets the needs of most residences, and a MERV 13 filter can last up to six months before needing to be replaced.
